In VLSI processes in which a high integration and a microfabrication are progressed, it has been positively prosecuted to establish effective mass productivity techniques as a concrete target for device production based on the design rule in submicron of 4M, 16M bit DRAM. In this connection, when metal wirings are formed on a substrate, it is necessary to solve the following three subjects:
(a) Reliable filling with metal film in a hole having high aspect ratio on the substrate;
(b) Formation of barrier metal;
(c) Establishment of a multilevel interconnection process based on a planarization technique.
To this end, various methods such as a bias sputtering, a selective growing of tungsten or etching-back method have been utilized. One of them, the selective growing of the tungsten is remarkably expected because it has a possibility of reliably forming and planarizing the metal film in the hole provided on the substrate, a barrier property of the tungsten itself and a high cost performance. It is known that the selective growing of the tungsten is one of chemical vapor deposition (CVD) methods in which a tungsten film is grown only on the Si surface or the metal surface surrounded by an insulating film such as SiO.sub.2, PSG, BPSG or the like.
There is known a hot wall type CVD apparatus comprising a lateral vacuum reaction chamber, in which a reaction gas inlet is provided on one side wall of the reaction chamber for introducing mixture gas of a gas containing a metal element, WF.sub.6, and a reducing gas, H.sub.2 into the reaction chamber, a reaction gas outlet is provided on the other side wall of the reaction chamber for evacuating the mixture gas of WF.sub.6 and H.sub.2, a substrate supporting plate is horizontally disposed in the reaction chamber for supporting a plurality of substrates longitudinally at a predetermined interval, and a heating electric furnace is provided on the outer periphery of the reaction chamber.
In this conventional CVD apparatus, when the reaction chamber is heated by the heating electric furnace, the wall of the reaction chamber rises at its temperature, the eat on the chamber wall is transmitted to the mixture gas introduced through the reaction gas inlet, and then transmitted to the substrates. When the substrates are heated by means of this heat transferring, a chemical reaction of WF.sub.6 and H.sub.2 occurs on the surface of each substrate to form a thin film on the surface of each substrate.
A procedure for forming the thin metal film on the portion of the surface of the substrate using the conventional system will be described.
As shown in FIGS. 1 to 4 of the accompanying drawings, Si substrate "a" is used on the surface of which the thin insulating film "b" of SiO.sub.2 is formed partially. Portions "c" of the substrate surface where no insulating film is formed is so-called contacting holes in each of which the thin metal film "d" is to be formed.
It is known that at the initial on the portions "c" chemical reaction occurs as follows: EQU WF.sub.6 +3/2Si.fwdarw.3/2SiF.sub.4 +W (1)
The thin metal film "d" is abruptly formed on the portions "c".
Then, it is considered that chemical reactions occur as follows: EQU 3H.sub.2 .fwdarw.6H (2) EQU WF.sub.6 +6H.fwdarw.6HF+W (3)
W is grown as time goes, and as shown in FIG. 3, the thin metal film "e" of W is formed on the surface of the thin metal film "d" of W initially formed.
In this case, the growth rate G of W is represented by the following: EQU G=(A)(H.sub.2).sup.1/2 exp(-Ea/kTm) (4)
wherein A is positive constant, (H.sub.2) is the concentration of hydrogen, k is Boltzmann's constant, and Tm is the temperature at the surface of the portions on which the thin metal film is to be grown.
The temperature Tm at the surface of the portions "c" becomes substantially equal to that at the surface of the thin insulating film "b". If the temperature Tm at the surface of the portions "c" is raised, as understood from the equation (4), the growth rate of W is increased, but temperature at the surface of the thin insulating film also raises. Consequently, on the thin insulating film "b" the chemical reactions as represented by the formulae (2) and (3) may also be occurred and thus a thin metal film "f" of W may be formed on the surface of the thin insulating film "b" as shown in FIG. 3.
In FIG. 4 there is shown in an enlarged version a part of the substrate shown in FIG. 3. It will be seen that, in the procedure of growing the thin metal film "e", there is occurred an encroachment phenomenon in which a metal element may be invaded into a boundary zone between the substrate "a" and the thin insulating film "b". As the case may be, voids "h" may be produced in the substrate "a". Such encroachment is denoted by reference "g".
According to the conventional method, the turbulent flow or the natural convection occurs near the substrate "a". The inventors have presumed that the turbulent flow or the natural convection accelerates the growth of the above-described encroachment or the voids.
However, the feed or stream of the gas is controlled only by two internal parameters such as pressure and reactive gas flow rate. Thus, it is impossible to externally control the gas flow so as to suppress the disturbance and the natural convection of the reactive gas which may be occurred in the reaction chamber. Therefore, thin films cannot be formed with excellent reproducibility, controllability and uniformity in wide pressure and flow rate ranges. Furthermore, since the reaction components are diffused in the entire area in the reaction chamber, it is not possible to avoid an adhesion of the diffused reaction components to the reaction chamber walls and an inspection window provided thereon. Therefore, the generation of dusts, the mixture of impurities in the thin film to be formed due to the adhesion of the diffused reaction components to the reaction chamber walls and the inspection window cannot be avoided.
To suppress such encroachment and the formation of the voids, a low temperature, low concentration growth has been developed. However, in this method, the growth rate which may be obtained is merely several 10 Angstroms/min. (see, by Broadbent et al. J. Electrochem. Soc. 131. (42) 1984; Blewer. VMIC 1985). For example, it takes approximately 2 hours to fulfill the contact holes of 1 micron depth.
In the conventional method, the growth of the W nucleus on the insulating film, that is, the selectivity loss may be easily occurred. To avoid this selectivity loss, it is necessary to see the growth rate of the W film at lower level or to decrease the thickness of the W film to be formed.
This invention is to utilize the combination of substrate heating source using infrared rays and a laminarized jet of reactive gas for purpose of maintaining the selectivity, facilitating the thin film forming reaction, and improving the high reproducibility and controllability.
The laminarized jet of the reactive gas has merits as follows:
(a) It is possible to coincide the gas flow control with a simulation;
(b) The diffusion of the reaction gas and reaction product to reaction chamber walls can be suppressed by uniformly and locally feeding the reaction gas to the vicinity of the substrate.
This invention has an object to provide a CVD apparatus which eliminates the disadvantages of the abovementioned conventional chemical vapor depositions, and can form a thin metal film only on a portion not formed with a thin insulating film in the surface of a substrate on which the insulating film is partially formed at increased growth rate while suppressing the encroachment and the growth of the voids.
Another object of the invention is to provide an apparatus for a chemical vapor deposition in which a thin metal film can be formed with good reproducibility, controllability and uniformity.